Background
The transmission line parameters are basic data of short-circuit current calculation, relay protection setting, transient stability calculation, load flow calculation, fault distance measurement and the like of the power system. If the parameter error of the power transmission line is large, many problems are caused.
1) The short-circuit current has a large calculation error, and the electrical equipment selected by using the result is not economical or is easily damaged under the short-circuit impact.
2) The relay protection setting value error is large, so that the protection overtaking action or refusing action is caused.
3) The power system stability calculation conclusion is inaccurate, and system instability can be caused.
4) The power system has large load flow calculation error and influences system planning, economic operation, network loss analysis and the like.
5) For the ranging method depending on the line parameters, the fault ranging error is increased.
At present, transmission line parameters are generally measured by using measuring equipment before commissioning. However, the parameters of the transmission line are influenced by factors such as geological, temperature, wind speed and earth resistivity along the line after the transmission line is put into operation, and the parameters can change. The online measurement of the transmission line parameters is widely researched for reflecting the accurate parameters of the transmission line under different operating conditions.
With the increasing popularity of the WAMS, there is a possibility to use PMU measurement data for line parameter identification. Chinese patent "a method for identifying power transmission line parameters" (application No. CN201210575136.6), "chinese patent" a method for identifying power transmission line parameters based on PMU data "(application No. CN201610839532.3) and" chinese patent "an on-line identification system and method for identifying power transmission line parameters" (application No. CN201710169327.5) all use voltage and current phasor values as known quantities to identify power transmission line parameters in the frequency domain, but the frequency domain method produces errors when extracting power frequency components, resulting in increased errors in identification results.
The fault recording data comprises rich transient state information, the fault recording data is used as a known quantity in a time domain, a differential equation describing a power transmission line model is written by utilizing a circuit law based on a power transmission line equivalent circuit model, and a least square algorithm is adopted to obtain a fault line parameter.
Disclosure of Invention
The invention aims to provide a fault line parameter calculation method based on single-phase earth fault recording data, which solves the problem of obtaining fault line parameters.
The technical scheme adopted by the invention is that the fault line parameter calculation method based on single-phase earth fault recording data is implemented according to the following steps:
step 1, acquiring fault data;
step 2, low-pass filtering;
step 3, calculating the current and voltage of the non-fault phase-to-phase line mode at two sides of the line;
step 4, calculating zero-mode current and zero-mode voltage at two sides of the circuit;
and 5, calculating the parameters of the fault line.
The present invention is also characterized in that,
the step 1 specifically comprises the following steps: when a single-phase earth fault occurs to a line MN, current and voltage sampling values at two sides of a power transmission line are obtained through a fault wave recording device or a relay protection device, wherein the sampling values comprise M-side A, B, C-phase electricityFlow rate ima、imb、imcVoltage quantity uma、umb、umcMagnitude of current i of A, B, C phases on N sidena、inb、incVoltage quantity una、unb、unc。
The step 2 specifically comprises the following steps:
and filtering the collected current and voltage sampling values by adopting a low-pass filter with the cut-off frequency of 100Hz, and filtering out high-frequency components.
The step 3 specifically comprises the following steps:
the non-fault phase-to-phase line mode current and voltage are obtained by the following formulas (1) to (4):
in the formula (I), the compound is shown in the specification,
is the voltage of the interphase line mode at the M side and the current of the interphase line mode,
the voltage and current of the interphase line mode at the N side are shown;
the voltage and current of the non-fault phase on the M side,
the voltage and the current of the N-side non-fault phase.
The step 4 specifically comprises the following steps:
the zero-mode current and voltage on two sides of the line are obtained by the following equations (5) - (8):
in the formula um0、im0Is a zero-mode voltage and a zero-mode current on the M side, un0、in0The voltage and current are zero mode voltage and zero mode current of the N side; u. ofma、umb、umc、ima、imb、imcVoltage and current of M side A, B, C phase, una、unb、unc、ina、inb、incVoltage and current of the N-side A, B, C phase.
The step 5 specifically comprises the following steps:
step (5.1), calculating a positive sequence parameter:
step (5.1.1), establishing a non-fault interphase line model pi-shaped equivalent circuit;
step (5.1.2), writing a differential equation of the equivalent circuit according to the circuit law as formula (9):
obtained by the formula (9):
in the formula (I), the compound is shown in the specification,
is the voltage and current of the M side non-fault phase-to-phase line mode,
the voltage and the current of the N-side non-fault phase-to-phase line mode;
is the first differential of the line mode voltage and the line mode current of the non-fault phase at the M side to the time t,
is the first differential of the N-side non-faulty phase-to-phase line mode voltage over time t,
second order differential of M side non-fault phase-to-phase line mode voltage to time t; r
1、L
1、C
1Positive sequence resistance, positive sequence inductance and positive sequence capacitance are to be solved;
step (5.1.3), substituting the non-fault interphase line mode current and voltage obtained in step (3) into equations (10) and (11), wherein the first order and second order differential are calculated by numerical difference, and the equation (10) is solved by adopting a least square algorithm to obtain the line positive sequence capacitor C1(ii) a C to be obtained1Substituting an expression (11), solving the expression (11) by adopting a least square algorithm to obtain a positive sequence resistance and a positive sequence inductance;
step 5.2, calculation of zero sequence parameters
Step 5.2.1, determining a fault position through a distance measuring device or manual inspection, and determining that the proportion of the length of the fault position from the M side bus to the total length of the line is alpha;
step 5.2.2, establishing a zero-mode R-L equivalent circuit of the fault line according to the fault position;
step 5.2.3, writing a differential equation of the equivalent circuit according to the circuit law as formula (12):
from (12), it can be obtained:
in the formula, alpha is the percentage of the distance from a fault point to a bus at the M end in the total length of the line; u. of
m0、i
m0Is zero mode voltage, current, u of M side
n0、i
n0Is the zero mode voltage and current of the N side;
is the first differential of the zero mode current of the M side and the N side to the time t; r
0、L
0Zero-sequence resistance and zero-sequence inductance to be solved;
and 5.2.4, substituting the zero-mode current and zero-mode voltage on two sides of the line obtained in the step 4 into a formula (13), calculating the first-order differential by using numerical difference, and solving the formula (13) by adopting a least square algorithm to obtain the zero-sequence resistance and zero-sequence inductance of the line.
The method for calculating the fault line parameters based on the single-phase earth fault recording data has the advantages that firstly, voltage and current data obtained by sampling after a fault are filtered, then an equivalent circuit model of the fault line is established, differential equations describing the circuit relation of all electrical quantities are written, the parameters of the fault line are calculated by adopting a least square method, the single-phase earth fault recording data is used for calculation, the phasor does not need to be extracted, errors caused by calculation of the voltage phasor and the current phasor are avoided, and the method is not influenced by frequency. The method can effectively calculate the positive sequence parameter and the zero sequence parameter of the fault line, and the error of the parameters is within 5 percent.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention relates to a fault line parameter calculation method based on single-phase earth fault recording data, a flow chart is shown in figure 1, a power transmission line model is shown in figure 2, and the method is implemented according to the following steps:
step 1, acquiring fault data, specifically: when a single-phase earth fault occurs to a line MN, current and voltage sampling values at two sides of a power transmission line are obtained through a fault wave recording device or a relay protection device, wherein the current values i comprise current amounts i of A, B, C phases at an M sidema、imb、imcVoltage quantity uma、umb、umcMagnitude of current i of A, B, C phases on N sidena、inb、incVoltage quantity una、unb、unc;
Step 2, low-pass filtering, specifically:
filtering the collected current and voltage sampling values by adopting a low-pass filter with the cut-off frequency of 100Hz, and filtering out high-frequency components;
step 3, calculating the current and the voltage of the non-fault phase-to-phase line mode at two sides of the line, and specifically comprising the following steps:
the non-fault phase-to-phase line mode current and voltage are obtained by the following formulas (1) to (4):
in the formula (I), the compound is shown in the specification,
is the voltage of the interphase line mode at the M side and the current of the interphase line mode,
the voltage and current of the interphase line mode at the N side are shown;
the voltage and current of the non-fault phase on the M side,
voltage and current of the N-side non-fault phase;
step 4, calculating zero-mode current and zero-mode voltage at two sides of the circuit, specifically:
the zero-mode current and voltage on two sides of the line are obtained by the following equations (5) - (8):
in the formula um0、im0Is a zero-mode voltage and a zero-mode current on the M side, un0、in0The voltage and current are zero mode voltage and zero mode current of the N side; u. ofma、umb、umc、ima、imb、imcVoltage and current of M side A, B, C phase, una、unb、unc、ina、inb、incVoltage and current for the N-side A, B, C phase;
step 5, calculating fault line parameters, specifically:
step (5.1), calculating a positive sequence parameter:
step (5.1.1), as shown in fig. 3, establishing a non-fault interphase line model pi-type equivalent circuit;
step (5.1.2), writing a differential equation of the equivalent circuit according to the circuit law as formula (9):
obtained by the formula (9):
in the formula (I), the compound is shown in the specification,
is the voltage and current of the M side non-fault phase-to-phase line mode,
the voltage and the current of the N-side non-fault phase-to-phase line mode;
is the first differential of the line mode voltage and the line mode current of the non-fault phase at the M side to the time t,
is the first differential of the N-side non-faulty phase-to-phase line mode voltage over time t,
second order differential of M side non-fault phase-to-phase line mode voltage to time t; r
1、L
1、C
1Positive sequence resistance, positive sequence inductance and positive sequence capacitance are to be solved;
step (5.1.3), substituting the non-fault interphase line mode current and voltage obtained in step (3) into equations (10) and (11), wherein the first order and second order differential are calculated by numerical difference, and the equation (10) is solved by adopting a least square algorithm to obtain the line positive sequence capacitor C1(ii) a C to be obtained1Substituting an expression (11), solving the expression (11) by adopting a least square algorithm to obtain a positive sequence resistance and a positive sequence inductance;
step 5.2, calculation of zero sequence parameters
Step 5.2.1, determining a fault position through a distance measuring device or manual inspection, and determining that the proportion of the length of the fault position from the M side bus to the total length of the line is alpha;
step 5.2.2, as shown in FIG. 4, establishing a zero-modulus R-L equivalent circuit of the fault line according to the fault position;
step 5.2.3, writing a differential equation of the equivalent circuit according to the circuit law as formula (12):
from (12), it can be obtained:
in the formula, alpha is the percentage of the distance from a fault point to a bus at the M end in the total length of the line; u. of
m0、i
m0Is zero mode voltage, current, u of M side
n0、i
n0Is the zero mode voltage and current of the N side;
is the first differential of the zero mode current of the M side and the N side to the time t; r
0、L
0Zero-sequence resistance and zero-sequence inductance to be solved;
and 5.2.4, substituting the zero-mode current and zero-mode voltage on two sides of the line obtained in the step 4 into a formula (13), calculating the first-order differential by using numerical difference, and solving the formula (13) by adopting a least square algorithm to obtain the zero-sequence resistance and zero-sequence inductance of the line.
Examples
If the power transmission line has A-phase grounding fault, calculating BC phase-to-phase line mode voltage and current u by using voltage and current sampling values at two sides of the linembc、unbc、imbc、inbc(ii) a Establishing a BC interphase line model pi-shaped equivalent circuit; writing a differential equation of the BC interphase line mode equivalent circuit according to a circuit law; will umbc、unbc、imbc、inbcSubstituting the differential equation; and solving by adopting a least square algorithm to obtain a line positive sequence resistance, a positive sequence inductance and a positive sequence capacitance. Determining the fault position through a distance measuring device or manual inspection; establishing a zero-mode R-L equivalent circuit of a fault line according to the fault position; writing a differential equation of a zero-mode R-L equivalent circuit according to a circuit law sequence; will um0、un0、im0、in0Substituting the differential equation, and solving by adopting a least square algorithm to obtain the zero-sequence resistance and zero-sequence inductance of the line.
And (3) simulating a certain 110kV power transmission system by using ATP/EMTP. The specific parameters are as follows: total length of transmission line is 30km, unit transmission line parameter r1=0.105Ω/km,L1=1.258mH/km,C1=0.0092μF/km,r0=0.315Ω/km,L0=3.774mH/km,C00.0031. mu.F/km. Zero sequence inductance L of M-side systemm011.6mH, positive sequence inductance Lm130.8 mH; n-side system zero sequence inductor Lm023.1mH, positive sequence inductance Lm1=61.6mH;Em=1.05∠0°,En1.00-30 degrees. The sampling frequency was chosen to be 4 kHz.
The results of the calculations obtained using the method of the present invention are shown in table 1. As can be seen from Table 1, the error of the calculation results of the positive sequence resistance, the positive sequence inductance and the positive sequence capacitance is small. Wherein R is1Error not exceeding 5%, L1Error of (3) is not more than 0.2%, C1The error of (2) is only 0.01%. As can be seen from table 1, although the calculation results of the zero-sequence resistance and the zero-sequence inductance are affected by the transition resistance and the fault location, the calculation error is small. Wherein R is0Error not exceeding 3%, L0The error does not exceed 0.5%. Therefore, the method provided by the invention has higher calculation precision.
Table 1 electric transmission line parameter calculation results